The efficiency of a data transmission from a transmitter to a receiver depends substantially on current information regarding the transmission quality of the data transmission channel used being available at the transmitter at the correct time. Only then can the transmitter match send parameters for the data due to be sent to the current situation in order to achieve satisfactory transmission results. Send power or modulation or coding scheme are regarded as send parameters, for example. The current information regarding the transmission quality is obtained from so-called “channel measurements” or “channel estimates”.
The problem with conventional data transmission is illustrated by way of an example using the UMTS standard (UMTS: Universal Mobile Telecommunication System). Refer to the description of the figures for explanations of terms used.
For UMTS, a packet,switched high-speed data transmission method has been proposed for a shared usage channel, the so-called HSDPA (High Speed Downlink Packet Access) method. Using this method, the receiver is a terminal and the transmitter is a base station. HSDPA provides for a slow signaling of control information through higher layers of the OSI layer model (OSI: Open System Interconnection), which controls the channel measurements for HSDPA.
The control information used for these channel measurements includes principally the timing rate for the measurements, the timing offset (displacement) with respect to a reference and the number of retries during the transmission of a measurement value. This means that after a radio connection or “radio link” has been established measurements are carried out at a fixed rate, regardless of whether and when data is actually sent on the shared downlink data channel HSDSCH (High Speed Downlink Shared Channel) set up for HSDPA.
Therefore, on the one hand, under certain circumstances a large number of unnecessary measurements are performed, while on the other hand there may be no current measurement present at the time of an actual packet data transmission, the so-called “packet call”. In this situation, a packet data transmission can include a plurality of individual packet calls which can in turn each comprise a plurality of individual data packets.
As a remedy, it has previously been proposed to take additional information about the status of the radio channel from the power control facility. This is, however, not possible for the situation where the terminal is running in so-called “soft handover” mode because it results in problems with the power control facility. “Soft handover” is understood to be a status in which a terminal is connected to a plurality of base stations. In this situation, the power is controlled such that the mobile station or the terminal is able to correctly receive the sent data with the aid of the signals received from all the base stations.
However, this does not generally mean that the terminal correctly receives the signal from the particular base station that sends out the HSDPA data. Since the HSDPA data packets are sent only by this one base station to the mobile station, the power control facility that is optimized for a set of base stations does not delivery any satisfactory additional information.
The following proposed prior art methods have therefore been put forward to solve the problems associated with current channel information data:
1. A so-called activity based channel quality information acknowledgment (activity based CQI feedback, CQI: Channel Quality Information). In this situation, the rate of cyclical measurements is increased as soon as the terminal device or terminal detects that data is being sent. With regard to a packet data transmission in accordance with HSDPA, an additional channel information message CQI can be sent particularly with each feedback indicating whether or not it has been possible to decode a received packet. This feedback can for example be a so-called “ACK”(Acknowledgment) or “NAK” (“No Acknowledgment”).
However, since a delay exists between the time when data activity is determined at the terminal, when the measurement is carried out and transmitted, and when the measurement is received and evaluated in the transmitter(in other words the base station), there are disadvantageous results for each packet data transmission. More specifically, for each packet data transmission the first packets have to be transmitted without a current channel information message or channel measurement. Furthermore, during an active data transmission, an unnecessarily large number of channel information messages are sent under certain circumstances due to the increased send rate for the channel information message, as a result of which unnecessary interference is generated in the uplink direction.
2. Another proposed method involves sending an additional channel information message after receiving a NAK. However, the same disadvantages occur here as described above.
3. Another method has been proposed whereby a channel information message is specifically requested. Although this allows this solves the problem associated with the absence of current information at the start of a data transmission (the explicit signaling on the HS-SCCH), the control channel for HSDPA does however result in an additional usage of resources in the downlink direction. It is also disadvantageous that delayed initial sending of the first packet of a packet data transmission occurs as a result of the explicit request operation.
4. Yet another method includes the terminal sending an additional channel information message precisely at the time when the terminal determines during the decoding process for example that the currently applied coding or modulation scheme is too good or too bad. For data links which are already active, this method ensures that channel information messages occur precisely at the time they are required and whenever they are required. A disadvantage of this method however is that the receiver of these channel information messages (in other words the base station in the case of HSDPA) does not know the points in time at which the channel information messages have been sent. As a result, detection and decoding of these messages is made more difficult.
To summarize, the disadvantages shared by all the proposed prior art methods is that it is not possible to simultaneously have access to current channel information and operate in a resource-efficient manner.